Japanese Patent Application No. 2005-52825 discloses a rotor in which a cogging torque is reduced and additionally a harmonic content in an induced voltage is reduced to thereby reduce a vibration and a noise. The rotor includes a rotor core and a plurality of permanent magnets. The plurality of permanent magnets is arranged annularly around a rotation axis. The plurality of permanent magnets is 15 embedded in the rotor core. The diameter of an outer circumferential side surface of the rotor core decreases at both ends of the permanent magnets.